(1) Field of the Invention
The invention is concerned with anionic structured particle latexes. The polymer particles comprising the latex have stabilizing, pH independent anions which are chemically bound at or near the surface of the particles.
(2) Description of the Prior Art
Latexes require some means for providing colloidal stabilization in aqueous media. The usual colloidal stabilization is provided by surfactants which usually are anionic or cationic but may be nonionic, especially in mixtures with anionic or cationic surfactants. Even though they contribute to the required colloidal stability, the surfactants can interfere with coating performance of the latexes even though the amount is limited and less than the desired stability is obtained. Another method is to copolymerize with nonionic monomers a small proportion of an ionic monomer to prepare a stable latex with little or no conventional surfactant as described in U.S. Pat. No. 3,617,368. Such processes, however, require special combinations of monomers and special polymerization techniques. Although such processes produce latexes having little or no surfactants, varying amounts of water-soluble products are made during carrying out of the process and remain in the product.
Aqueous colloidal dispersions (latexes), stabilized by adsorbed interfacially spreading polyelectrolytes, are described in U.S. Pat. No. 3,965,032. Latexes made by that approach have excellent stability and are particularly useful in applications like coatings where conventional surfactants interfere with performance. However, in some cases (e.g., beater addition), the adsorbed polymer layer can be desorbed causing interference with deposition and thereby limiting utility.
Latexes containing generally less than a monolayer of pH independent anionic groups attached to the particle are described in U.S. Pat. No. 3,640,992, issued to David P. Sheetz. Other previous methods available for introducing pH independent anionic groups, such as by reactions at the latex particle surface, are slow and inefficient in comparison with cation forming reactions and the maximum amount of charge that can be introduced by these methods is low. The latexes require further stabilization by added conventional surfactants in order to be useful in many applications.